1. Field of the Invention
The present invention relates to a shaft for a roller wheel which is used in a roller wheel of a crawler type traveling apparatus or the like.
2. Description of the Prior Art
As shown in FIG. 15, there has been conventionally a crawler type traveling apparatus (a chassis apparatus) structured such that a frame 101, an idler 102 and a sprocket 103 are arranged approximately linearly, a plurality of lower roller wheels 104, . . . are rotatably provided in a lower portion of the frame 101, and a crawler belt 105 is wound around the idler 102, the lower roller wheels 104, . . . and the sprocket 103. The lower roller wheels 104 are structured such as to disperse a weight, of a vehicle body and transmit to the crawler belt 105.
In this case, the lower roller wheel 104 is provided with a shaft 106, and a roller 107 rotatably supported to the shaft 106, for example, as shown in FIG. 16. The shaft 106 is constituted by a first shaft portion 108a and a second shaft portion 108b, and the first shaft portion 108a and the second shaft portion 108b are integrally welded. In other words, the respective shaft portions 108a and 108b are constituted by large-diameter main body portions 109a and 109b, and supporting portions 110a and 110b continuously provided in the main body portions 109a and 109b, and hole portions 111a and 111b are provided in the main body portions 109a and 109b. Further, the main body portion 109a of the first shaft portion 108a and the main body portion 109b of the second shaft portion 108b are integrated in an abutted state. Further, the roller 107 is rotatably outward fitted to the main body portion 109a of the first shaft portion 108a and the main body portion 109b of the second shaft portion 108b via a bearing means.
Further, there is a shaft which is not joined (for example, patent document 1). The shaft mentioned above is called as a dumbbell type, as shown in FIG. 17. In other words, in this case, the shaft is constituted by supporting portions 113a and 113b in both end portions, and a large-diameter portion 114 in a center portion, and a peripheral groove 115 is formed in a center portion of the large-diameter portion 114 in an axial direction. Further, the roller 107 is rotatably outward fitted to the large-diameter portion 114 in the center portion via a bearing means.    Patent Document 1    Japanese Unexamined Utility Model Publication No. 5-45338 (page 1)
However, since the shaft is formed in a hollow shape in the case of using the shaft in FIG. 16, a weight saving can be achieved, however, it is necessary to join the first shaft portion 108a to the second shaft portion 108b. It is troublesome to manufacture such the shaft, and if there is a defect in the joint of the joining area, there is a risk that the first shaft portion 108a and the second shaft portion 108b are separated from each other at a time when a load is applied during use. Further, in the dumbbell type as shown in FIG. 17, it is possible to avoid a joining work, however, since the shaft is a so-called solid type, the weight is increased, and a cost thereof is increased accordingly. Further, in order to supply an oil to an oil reserving portion 116 formed between a roller inner peripheral surface and a shaft outer peripheral surface, it is necessary to form diametrical hole portions 118 and 118 communicated with an axial hole portion 117. The diametrical hole portions 118 and 118 reach an outer peripheral surface from an axis O and are comparatively long, and it is troublesome to work the diametrical hole portions 118 and 118.